Various analytical instruments execute processes in which an amount of a sample material is placed on a slide for further processing or examination. Such slides include standard laboratory glass microscope slides. Typically, these standard slides are about 1″×3″×0.04″ in size and are packaged in a box of 72 slides each. Three packages of these slides are normally stacked vertically on the instrument. The slides are then individually introduced to the instrument by removing a single slide from the bottom of the stack.
Removal of the slides from the bottom of the stack can be quite problematic. The friction caused by the weight of the slides in the stack and the vacuum created between the slides because of their smooth finish result in the bottom slide sticking to the slide immediately above it. This problem is exacerbated when an amount of moisture from condensation gets between the slide surfaces.
An apparatus having an extractor unit adapted to remove a slide from the bottom of a slide stack is illustrated in U.S. Pat. No. 6,319,470, entitled “Device for Automatic Preparation of Blood Smears on Plates” and issued to Lefevre et al. The slide extractor unit shown in the '470 patent includes a thruster having a blade that is displaced linearly in the direction of slide extraction. The slide stack is presented to the slide extractor unit at an angle so that the longitudinal edge of the slide engaged by the blade is at a slight angle relative to the direction of extraction. In accordance with one embodiment, the angle is 3°, such that the longitudinal edge of the slide forms an angle of 93° relative to the direction of extraction. According to the '470 patent, installing the stack of slides with angular offsetting of this type permits more efficient detachment of the slides and limits blockages or slowing down caused by slides adhering together.
Despite the purported mechanical advantage associated with the foregoing apparatus, a significant amount of force is still required to extract a slide from the bottom of a slide stack. The removal force is initially focused on only a small portion of the longitudinal edge of the bottom slide and can cause the slide to break. Still further, no provision is made for slides that break under this force. Additionally, implementation of the foregoing apparatus typically results in complex mechanisms that are difficult to build and service. The present inventor has recognized a need for an improved ejector apparatus that addresses many of these deficiencies.